The present invention relates to electrical switches having contacts that move from a first state to a second state when acted upon by an actuator; and more particularly to such switches which include a reset mechanism for returning the contacts to the first state when no longer acted upon by the actuator.
U.S. Pat. No. 5,565,666 discloses a switch for interrupting an electrical circuit in response to a mechanical condition, such as an over pressure or under pressure condition detected in a conduit. The switch includes a support arm that is electrically connected to an electrical terminal and movable between a first position and a second position in response to the mechanical condition. The switch includes a snap action blade operatively connected to the support arm. The snap action blade levers from a first configuration to a second configuration when the support arm moves from the first position to the second position. In the first configuration, the snap action blade disengages a contact connected to another electrical terminal to interrupt the electrical circuit. The snap action blade engages the contact to complete the electrical circuit in the second configuration. The snap action blade is stable in both the first and second configurations and remains in the respective configuration until acted upon by an external force.
This type of switch further includes a reset actuator disposed to engage the snap action blade in response to manual activation. The snap action blade levers from the first configuration to the second configuration only when the reset actuator engages the snap action blade and the support arm is not in the second position. Thus the only way in which the snap action blade can be returned to the second configuration to complete the electric circuit is upon manual activation of the reset actuator. This reset is referred to as being "manual" in that it requires activation of the reset actuator even though such activation may be controlled by a mechanical actuator which does not require human intervention.